Method of improving frictional contact between metal surfaces normally in rolling contact and resultant structure



METHOD OF IMPRVEJG FRICTIONAL CNTACT BETWEEN METAL SURFACES NRMALLY IN glNG CONTACT AND RESULTANT STRUC- George W. Luvis, Chicago, lll., assignor to National Alunnnate Corporation, Chicago, lll., a corporation of Delaware Application September 8, 1955, Serial No. 533,190

43 Claims. (Ci. 104-1) This invention relates to a new and improved adhesion treatment of metal surfaces and more particularly to a method and cornposition for increasing the coeflicient of friction between metal surfaces capable of motion one with respect to the other. The invention is especially concerned with the provision of chemical means for preventing wheel slippage between locomotive wheels and rails. However, in its ronder aspects the invention contemplates the improvement of frictional contact between metal surfaces which are susceptible of slippage one with respect to the other, as, for example, the slippage which occurs between a shaft and a sheave, gear or pinion frictionally mounted on said shaft.

The past several decades have produced railway locomotives possessing great power and weight, thus enabling long, heavily-laden trains to be pulled by single engines. vVith the advent of the extremely heavy locomotive it was felt that driving wheel slip would be eliminated. It was soon discovered, however, that the increased static weight carried on the driving wheels did not solve the problem to any great extent. Track sanding techniques were developed but this only partially alleviated the condition. Wheel slippage has proven to be an erratic condition which has not in all cases been satisfactorily explained.

in one explanation of the problem, rail slip is said to result from a tough invisible oil film on the wear band of the rail. Traffic and heat destroy this film and high adhesion results. When a light rain occurs or when the rails reach the dew point, as the result of the relatively high humidity, a water film forms across the wear band where it may contact oil deposits on the edge of a rail with the result that a film of oil creeps through and replaces the water film. The oil deposits on the rail sides act as reservoirs for the formation of new oil films and water acts as the transporting agent. The oil deposits on the rail come from journal box oil leakage by way of the outside face and outer portion of the tread of the car wheels. There are other sources of contamination such as road crossings, rail lubricators, and the like.

The importance of solving the problem is strinkingly illustrated when it is realized that only 15% of the engine's weight can be utilized as tractive force when the rails are greasy and moist, and 30% when the rails are clean, dry and sanded. Even a small improvement in these figures, as expressed in the terms of increased coefiicient of friction, would enable railway locomotives to operate more eificiently and economically as well as providing improved braking for railway locomotives and rolling stock.

Another instance where it is desirable to improve the frictional contact between two metal surfaces capable of motion one with respect to the other is where a gear or pinion is frictionally mounted on a shaft. Obviously, if slippage occurs between the gear or pinion and the shaft the eiciency of the particular operation in question is reduced or the device may even become inoperable,

lt is therefore an object of this invention to provide a new and improved method for enhancing the frictional contact between two metal surfaces capable of motion one with respect to the other.

Another object of this invention is to provide a method for raising the coeflicient of friction between railway car wheels and rails.

Still another object is to raise the coefficient of friction between railway car wheels and rails having an oil film thereon.

A further object is to provide a method of decreasing slippage between railway wheels and rails.

Another object is to provide a chemical treatment to prevent locomotive slippage on dry, wet, or oly rails.

Still a further object is to enable railroad locomotives to utilize more of their tractive forces on wet oily rails than has heretofore been considered possible.

An additional object of the invention is to produce a railway rail containing an adherent coating of a material which substantially prevents slippage between the rail and a locomotive or railway car wheel.

Still a further object is to provide a method of substantially preventing slippage between the hearing surfaces of a railway rail and a locomotive or a railway car wheel by applying to the rail and/or wheel a liquid coating material which evaporates leaving a thin film or coating of a slip inhibiting Substance.

A further and more specific object of the invention is to provide a new and improved method for improving the frictional contact between a metal shaft and a sheave, gear or pinion frictionally mounted th'ereon.

Other objects will appear hereinafter.

in accordance with the invention, it has been found that the coefi'icient of friction between metal surfaces capable of motion one with respect to the other can be increased by applying to the Contacting surfaces thereof a thin film of colloidal Silica. The invention in its pre-' ferred embodiment is particularly applicable to improving the coefficient of friction between railway car wheels and tracks by applying to at least one of the contacting surfaces thereof a film of colloidal silica.

In the drawing a single figure shows a section of a railway rail containing a coating consisting essentially of colloidal silica applied to the hearing surface thereof.

As shown in the drawing the rail 1 has a hearing surface 2 to which the coating of colloidal silica 3 is applied. The coating of colloidal silica may also extend over the surface 4 which comes into contact with the wheel flange of the wheels of locomotives and railway cars.

An important feature of the present invention resides in the fact that silica in colloidal form adheres to steel rails. Furthermore, colloidal silica is a hydrous oxide and can be prepared in a liquid carrier medium, such as water, in the form of a silica sol. When a silica sol is applied to the bearing surface of a steel rail, the evaporation of the water or other liquid carrier medium leaves a thin strongly adherent film or coating which has pronounced anti-Slip Characteristics. In the simplest method of practicing the invention, therefore, an aqueous solution of colloidal silica, that is to say, a silica sol, is applied either to the steel rail or to the surface of a locomotive wheel or railway car wheel or to both the rail and the wheel. In most cases, however, the coating of colloidal silica will beapplied to the rail by carrying or swabbing or by any other suitable mechanical or physical means. The colloidal silica can also be applied in paste or solid stick form, admixed with other substances such as, for example, silica flour, and finelyy divided kaolin.

If the colloidal silica dispersed in a liquid medium is applied to a metal surface such as a locomotive Wheel, it is desirable that the product be dry or semi-dry by the o time the wheel contacts the rail. To this end the application of the liquid containing the colloidal silica is advantageously efected by a method involvng blowing with v0.1' .other gas which .assists in the evaporation of a -volatile liquid Lin which .the colloidal silica is dispersed. If the .colloidal .silica is .in the form of a fine .silica powder it can be applied to the metal :surface separately, either simultaneously .or contemporaneously, with a 'liquid which assists in forming .a coating of .the colloidal .silica on the metal. The colloidal silica can also be .converted to a semi-sol, gel, or paste and :applied in such form by applieators .suited for the application of gel-like or pasty materials.

.colloidal .silica -occurs in various .forms and .it will be understood that all forms 4of .colloidal .silica .do not give the .same results .in the practice of the invention. Some forms Vof colloidal silica, such as silica sols containing about 7% .to about 48% by weight .of .SiOz are especially advantageousfor the practice of the invention. The colloidal silica in these sols preferably has a particle size within the range of 1 millimicron .to 150 millimicrons. The partiolesize can be varied, dependent upon the method .of preparation as hereinafter described. These sols can valso contain stabilizing agents as hereinafter described.

ln general, the colloidal silicas, preferably employcd in the practice .of .the .invention .fall into three classes:

A. The silica sols.

LB. The colloidal silicates, and

C. The hydrolyzed organic esters of silicic acid.

A. THE SILICA SOLS VSilicjic acid sols are generally believed to be a polymeric derivative of monomeric silicic acid which arbitrarily may be assigned the formula As this material is produced it is .Capable of polyrnerizing to :form various sized polymers containing .the mer unit if the mechanism is considered linear. It is known, however, if the reaction carries to completion a gel is formed which evidences a three .dimensional cross-linked network formed from the starting silicic acid molecule. The polymerization :mechanism thus described may begin immediatejly upon the formation of rnonomeric silicic acid .and proceeds to form particles or masses of colloidal size within a very short time. With the silica sols preferred for -the practice of this invention when colloidal dimensions have been formed the cross-*linking or gelation of the sol may be inhibited by adjusting the pH of the system with acid or alkali to between '2.5 to 4.8 and 8.5 to 10.6, respectively, or adding a small amount of alkali metal. Under these conditions, lthe sol will retain its colloidal dimensions for long periods of time. When the silicic acid reaches colloidal size and is stabi'lized, the particle sizeV present is about l Vrnillimicron and possibly 2 to 3 nnllicrons in diameter. The exact size will depend on concentra-t-ion, presence or absence of electrolytes, lpH and temperature.

The l-silieic -acid sols preferably employed in the present invention are those containing at least 3.0% SiOz and a pH suflicient to stabilize said sol against gelation. Silicic acid sols may be prepared by any number of -Well known methods, many of which are summarized in Bechtold, et a'l.,'-U. S. Patent 2,574,-902, and thepi'esent invention contemplates the use of Vany of such solsI Silica sols capablc of luse in the :present invention lmay 'be convenientl-y prepared by the techniques described in Bird, U. S. Patent 2,244,325, although the well 'known method of hydrol-yzf ing sodium silicate with strong mineral acids with the subsequent removal of excess salt is equally suitable.

The Bird patent shows that alkali metal silicate solutions may be contacted with a cation exchange resin in the hydrogen form to produce a silicic acid sol of relatively high purity. After the sol is produced it may be stabilized with a small amount of alkali metal to impart to the finished sol, a high degree of stability. LSilica (SiOz) to alk-a-li metal (calculated as NaaO) weight ratios .of V50.:1 to lOGzl are preferably employed to impart such stability.

The stabilized sols produced by 'Birds .method .are capable of use in the practice of the present invention as produced or they may be concentrated to increase the silica content thereof, .several folds. While the Bird patent shows generally the method of concentrating silica sol-s, there are now several .methods available which produce sols having a relatively high silica concentration in the form of discrete non-agglornerated particles. Such methods are shown in Bechtold et al., U. S. Patent 2,574,9{)2, Brage et al., U. S. Patent 2,6SG,721 and i arma et al., U. S. .Patent 2,601,235.

In concentrating colloidal silicic acid sols, the -usual methods increase the size of the discrete particles present in the sol. As the general rule the more concentrated the sol, the larger will .be the particle size of the silica present., In a freshly prepared 'batch of stabilized 35% by weight SiO? sol prepared by the Bird method the particfle size is believed to be about 1 to 3 millirnicrons in size. f such a sol is concentrated to say about 39% SiOz by using the techniques of Bechtold et al., U. S. 2,574902, the average particle size will vary from 15 to millirnicrons in diameter.

As can be seen from the previous discussion a wide variety of colloidal silica in the form of aqueous sols are readily capable of being prepared. The invention .will be further illustrated by the following examples in which the proportions are given by weight unless otherwise indicated. A11 of the colloidal silica compositions described in these examples vare suitable for the practice of the invcntion.

Example I contained about 35% SiOz, had a pH of 3.5 and a cnni ductivity of about 400 to 809 micromhos. To this silicic acid sol elfluent was added an amount of 26 aurn ammonium hydroxide .sufiicient to adjust the pH of the acid sol to about 9.0.

Exzmple II The procedure used in Example l was the same .except that the solution .of the starting sodium silicate .containcd about 10% Si02. The :finished sol Ihad an SiOg concentration of about 7% and a specific gravity of about 1.059. Ammonium hydroxide ywas added to the sol so that the finalvpH was about 10.5.

Example ll! A portion of the sol of Example .I was placed .in .an evaporating kettle .and heated until ammonia and steam vapors began to come off. At this point a small amount of permanent alkali (KOH) was added and fresh arnmonia stabilized sol was added to maintain the evapcrating volume constant. Throughout the process the pH was never lallowed to go below 8.5. This was accomplished by continually adding gaseous ammonia duringV the heating process. The constant evaporation lWas conpH always above 8.5, and was continued until specific .fa/:sasse gravity of the sol had reached 1.20 at 68 F. When this specific gravity had been obtained an amount of potassium hydroxide Was added to give the finished sol a pH of 9.0. This sol had an SiOz concentration of 30%.

Example IV Another sol was produced by using the method shown in Example III. In this instance, however, the concen- -tration process was continued until the sol had an SiO2 concentration of about 48%.

In general, the silicic acid sols are preferably used in their more concentrated form. Sols containing about 30% SiOz have given superior results, yet sols having an SiOz content as low as 3% have shown effectiveness. Dosages in the amount of 1 to 5 gallons per two rail track mile are usually adequate.

These aqueous sols are sensitive to low temperatures but they may be treated by two methods whereby the effects of lower temperatures are avoided. The first method is to incorporate therewith an antifreeze such as v i, U; s. Patent 2,6o1,291.

Inorder to facilitate application of the sols to afford a more even distribution over the surfaces of the railway car Wheels or rails, it is helpful to add thereto about 0.1% to 2% by weight of a compatible wetting agent. The only requirement of such agent is that it be compatible With the sol insofar as it is soluble and does not cause precipitation or gelation. Anionic synthetic detergents of the alkali metal alkyl (e. g., octyl or nonyl) benzene sulfonic acid type are admirably suited for the purpose of the invention. Any compatible anionic or non-ionic wetting agent can be employed, for example, those listed in the article Synthetic detergents-to date, II, by John W. McCutcheon, appearing in Soap and Sanitary Chemicals, July, August, September and October issues, 1952. Cationic wetting agents tend to form gels or precip-itates when added to these sols and should be avoided.

B. THE COLLODAL SILICATES The colloidal alkali metal silicates or waterglasses are usually produced commercially by fusing soda ash and sand at a temperature of about 1300 C. Theamount of alkali to silica may be. varied by several well known methods thus enabling production of water soluble silicates of a wide variety of properties and characteristics. The colloidal Waterglasses, however, usually have an alkali metal oxide ratio (expressed as NazO) to SiOz of not more than about 1:2, and generally less than l:2.2. Sodium silicates having an Na2O:SiO2 ratio of 1:3.22 to 1:3.86 have improved the coeflicient of friction between Contacting metal surfaces as shown in the test methods hereinafter described. As the NaO2 to S102 ratio decreases, the solubility in water decreases. For instance, a sodium silicate having an NazO to SiOz ratio of 1:2 can be concentrated to about 54% solids whereas a 1:3.2 material is only feasibly handled in concentrations below 40% solids. While the ratios shown above could theoretically be changed indefinitely, a ratio of about 1:4 sets the approximate lower limit since the materials become too difficult to manage-and must be diluted before being capable of use.

Commercial forms of colloidal alkali metal silicates are usually liquids and are conveniently used in this invention as supplied. They have a Baum gravity of from about 35.0 to 59.3 with the lower gravities being indicative of thehigh SiOz materials. While the liquid silicates' are conveniently handled as furnished by the manufacturertcare m ust be taken to prevent Water loss.

TAB LE I Approx. Ratio, NazO S102 Baum,

Vlscoslty Degrees Poises POTASSIUM SILICATES Degrees Viscosity, Poises SOLID SOLUBLE SODIUM SILICATES Percent SiOi Rato, Na20:Si02

Content in using these materials theyare preferably applied in a concentrated form or may .be diluted with water to about 15% S102. Applications are made to one mile of two rail track using 1 to 5 gallons on the track surface. It -is to be understood that the smaller the NazOzSiOx ratio, and the more concentrated the solution, the smaller will be the amount of colloidal alkali metall silicate required. ln any event, it is to be understood that the amount used is dependent on various conditions and is predicated on the amount suiicient to improve the coefficient of friction for any given set of such conditions.

C. THE HYDROLYZED ORGANIC ESTERS OF SILICIC ACID Another' source of colloidal silica for use in the practice of the invention are the hydrolyzed organic esters of silicic acid. These esters are usually prepared by the reaction of an organic compound having a free hydroxyl group with SiCli. This reaction is shown by the following equation where R is a hydrocarbon group.

The organic hydroxyl containing compounds are usually low molecular weight acyclic aliphatic aloohols having not more than 6 carbon atoms and aromatic hydroxyl compounds such as phenol. If the condensation reaction above is carried to completion under substantially anhydrous conditions the tetra substituted alkoxy or aroxy silane Will usually result. If, however, the esterification is incomplete or water is present, a condensed ester of the general formula (RO3)Si-O(Si-O)n-Si(ROs) Will result where n is a small whole number and R is a hydrocarbon radical." Examples1 of several commercially available ethyl silicates are shown in Table II below.

arsa-ses 2'I'ABLE II I Tetraethyl Ortho Condensed Ethyl i -Ethylfl(40% -SiOaD Sillcate Sllicate Silieate Molecular Weight Speclfie Gravity at 20/20 C 03323 1-0503- f Btyelow 100 C i' v 57 max. 5 max. eow" Bonm Billiee, 760 mm- He {Bw 170 C Bglow 190 C .5% max. Available Silica ns S10; Freezing Point, C Average Weight per gallon at Vlscosity at 20 O., cps Reractive Index-at 20 -C.-72D Flash Point (Cleveland open cup) 98% -tetraethyl-sllicate.

'In addition to those si'licates shown above, others that -rnay be used are methyl silica-te, Vbutyl silicate, amyl silicate, phenyl silicate, benzoyl silicate, hexamethoxytlisiloxane and hexaethoxydisiloxane.

All the s-ilicic acid esters shown above have the property -of hydrol-yzing in water, or water alcohol niixtures at rather uniformly controllabjle rates. A small amount (0.03 to 01%) of a strong mineral acid -such as hydrochloric will accelerate the 'hydrolysis reaction. When -less than the equivalent amount of water is used in an alcohol solution of these silicates they can be stored for long periods of time without gelation. Examples of hydrolyzed ethyl silicate solutions are given in the publication Ethyl Sil-icates January 4, 1954, by -Carbide and Carbon Chemicals Company. While some of the cornpounds shown above are esters of polyrner-ic silicic acid they are herein considered to be simply esters of silicic acid.

EVALUATION OF THE INVENTION In order to evaluate various colloidal silicas as agents for improving the .coeicient .of friction between railway car wheels land rails, the following test apparatus was employed.

A steel rail was used as the base surface upon which the Itest Was run. A :U-shaped member made of heavy strap steel Was formed *having two perpendicular pieces attached to the tips of the v U. A figg diameter hole was bored'in the center .of the base of the U. A 1% diameter stecl'ball having a "Brine'll'hardness of 500 was welded to a threaded steel rod. 'The threaded steel rod was placed in the jhole 'formed in 'the U-shaped steel member and fastened .with a nut'so that the steel ball was within the -cradle of the U. The perpendicular arms Were fitted V with small steel 'boxes capable of holding lead VShot or other weighted material. The U-shaped member was placed on the rail so the steel ball rested on the surface of the rail. To either side of the inverted U, wires were attached at a point slightly above the rail surface. Fixed to the other cnds of the wire was a short piece of string that passed over a fixed pulley, the top of Which was approximately coplanar with the surface of the rail. At then-opposite end of 'the string was a' suspended conminer which -could be fil-led Iwith weights.

In operation, the boxes were filled with lead shot in an amount which, when included with the weight of the cradle and fixtures, exerted a pressure at point of contact on the rail of 73,900 pounds per square inch. The weight of *the U-shaped member and ball was 3,065 grams, which, for the purposes of experiment, may be considered .as lthe operative dowmvard pressure. The suspended container was filled Vgraclually with lead shot until the steel 'ball 'just started to slide. This amount of weight is considered as 'the *force necessary to overcc/me the friction existing between the ball and the rail. Using these .two factors, .the coeicient of friction may readily be evo'lved from the Vfollowing simple equation:

of l5-9,200 vpounds per square inch, a percent elongation of 173% land a decarburization to a depth of 0.008. An analysis of this steel showed vit to contain .the following:

Percent Carbon i .311

Ivanganese .58 Phosphorous :016 Sulfur .016 Silicon .29 Chromium 11000 Molybdenum :22

In using .each .of .these vsurfaees the .blank .tests .did not vary within experimental error and hence the test :method was concluded to be standardized throughout.

At the start .of each .series of :tests the :ra-il and ball were cleaned with-scouring powder, rinsed with distilled Water and dried with cellulose tissues. Periodic inspections were made of the Contacting surfaces and when scratches occurred the ball and rail were polished with emery paper to renew the surface finish.

To simplify the experimental results the forces necessary to overcome the 1friction of the steel ball on 'the rail were recorded in grams. 'Three types of blank tests were run, the first being conducted vwith clean d ry surfaces. .The average of 10 such tests showed a force of 1835 grams necessary to move the ball. :When ka visible film of journal 'box oil was applied to Ithe rail the average was 620 grams. When 4water wasapplied to the oil film the average was found .to ;be 720 grams.

After a number .of tests it was determined that .tests on the oiled rail alone were su'fiicient for purposes of comparison.

Listed below are .several coinposit'ions that were tested. The results, which are .averages of two or more runs, are show-n in Table III:

Composition A: Sodium salts o'f an alkylbenzene sutfonic acid, 20% solution. The alkyl groups iin this Composition contain about 8 toV 12 carbon atorns Composition B: Rubber paint Composition C: Sodiurn metasilicate (NazOzSi'Qz of vIt had a tensil e strength of 164,2,00 pounds vper .square ainch, a yie1d,point arsa-961,8

Silica sol of Example III l percent 99.9

25% solution of Composition A do 0.1 Composition M:

Silica sol of Example III ml-- 50 Methanol ml 50 Citric Acid a gram 1 This gave a sol having a freezing point of C. Composition N:

Composition M -sunpercent-- 99.9

Composition A do 0.1 Composition O:

Silica sol of Example III ml-- 75 Methanol ml-- Citric Acid grams 2 This gave a sol having a freezing point of -15 F.

Composition P: Silica sol of Example IV diluted to 7% SiOz Composition Q: Silica sol of Example III diluted to 7% SiOz Composition R: Sodium silicate (NazOzSiOz of 1:3.2)

37.5% SiOz Composition S: Composition R diluted to 19% Si02 Composition T: Sodium silicate (Na2O:SiO2 of 1:3.75)

' 27% SOz In the following table Oiled Surface-wet" means that the anti-Slip composition was applied to the oiled surface as a liquid and the test was conducted before the coating was allowed to dry. The heading Oiled Surface-Dry means that the coated test piece was allowed to dry and then tested. I

TABLE III Grants Force to Cause Slippage Test No. Composition Oiled Surface Dry Surface 'Wet Dry Blank 1,835 620 1 Average of 11 consecutive runs. 2 Continuation of 13 with fresh oil coat applied. Average of 10 consecutlve runs.

From the results shown in'Table III it can be seen that from the large variety of materials tested, Compositions F, G, H, J, L, M, N, O, P, Q, R, S and T were superior.

In order'to further evaluate the compositions of the presentinvention field tests 'were run under actual railroad Operating conditions.

i 10 g Example V The test engine used was an Alco diesel 1000 horsepower switcher type pulling thirteen freight cars. The test was run during the winter months and the temperature for the day of the test was about 40 F. with the sky being bright and clear. Six rail lengths of track were oiled with a mixture of diesel fuel and lube oils by Wiping a rag saturated with the oil mixture along the top of the rail. One rail length was skpped and another six rail lengths were oiled in the same manner, To the second section of track a thin coating of Composition G was applied over the oil film by passing an applicator wet with the Composition G along the top of the rail. Composition G was allowed to dry and formed a barely visible film.

In order to increase the load on the switcher engine the brakes Were set onlthe freight cars and the throttle opened wide on the engine. Operating under these conditions on the oiled but untreated rail, the engine was unable to move forward, the wheels spinning freely. To get the needed traction to move off the oiled rail the car brakes were released, the throttle reduced and sand was used. Even under these conditions forward motion was barely sustained.

When the engine, with full throttle and the brakes set on the freight cars started on the Composition G treated section of track, there was no wheel slip and the train readily picked up speed and moved forward. The contrast between the traction obtained on the untreated and treated oil track was very sharp. There was no visible wheel slip in the latter case.

Example VI The same conditions shown in Example V prevailed except that Composition G was applied to the rail and the test run was run before the composition had dried. In this case Composition G appeared to reduce but not eliminate slippage. The train was able to sustain forward motion but there was some wheel slippage.

Example Vll The test conditions were similar to those shown in Examples V and VI above. The test equipment consisted of two 1000 horsepower Alco switcher diesel engines pulling twenty-seven loaded ore cars. Plain water was applied with an applicator to six rail lengths of track directly in front of the train. In starting, there was some wheel slip even on the dry rail, but when the switcher engines reached the wet track there was considerable slipping and the train proceeded with difficulty. The train was backed up and Composition F was applied to the wet rails with applicators. Immediately afterwards, while the rails were still wet, the train started over the treated section with no visible wheel slippage. There was no doubt that Composition F, while still liquid, had transformed a condition of wheel slip into that of no wheel slip.

Example VIII The conditions were the same as Example VII, Composition F was applied to six rail lengths of track with an applicator and allowed to dry. The dried film was. not as thin or as continuous as that in Example V. j

The train started and proceeded on the treated section with no wheel slippage. In comparing Examples VII and VIII it was generally concluded that the dried Composition F gave better adhesion (i. e., less slippage) than the wet material.

Example IX The composition tested consisted of a liquid made by adding orthophosphorc acid to a silica sol prepared by the ion exchange method containing 35% SiOz in water until the pH was 3.5 and then adding isopropanol until.

l 1 the isopropanol content was 50% by volume of the total volume, hereafter referred to as Composition U.

The resultaut composition was tested in actual railroad operation both by applying the composition to the wheels of the locomotive and by applying it to the rail.

The test equipment installed on the locomotive units consisted of one single and one dual recording meter and a transition indicator. The single instrument, an ammeter, was mounted in the cab of the leading locomotive unit and connected to record the current in the first traction motor. The dual instrument was installed in the cab of the trailing unit. The voltmeter and ammeter elements were connected across the main generator so that the main generator voltage was recorded. The ammeter was connected to a shunt which was inserted in the main generator lead to the traction motor.

An indexing needle on both tapes of the dual meter was fitted with a push button which recorded mile posts for identification. A second indexing needle on the ammeter was connected in a wheel slip relay circuit to record wheel slips. A second indexing needle on the voltmeter Was connected across the sander circut to record sanding operations. In addition, a transition indicator light was installed in the cab of the trailing unit. Observers in this cab kept a minute-by-minute log of motor current, speed and other pertinent data.

Traction motor torque was calculated from meter readings and the motor characteristic curve by the formula:

:motor torque in foot pounds k=factor to convert electrical to mechanical units Ia=motor armature current f ==magnetic flux (from motor characteristic curve) The corresponding tractive effort was:

TxG. R. (2) T' E' o.5 W. D.

Where T. E.=tractive effort in pounds T :motor torque per axle, (1) above W. D.=wheel diameter in feet G. R.=motor gear ratio Adhesion then was:

Where F=adhesion factor in percent W=weight per driving axle in pounds Thus, it was possible to obtain a continuous record of adhesion being developed by the locomotive and limiting adhesion at the time of a wheel slip.

The rails Were sprayed With the previously described rail conditioning composition from. a motorcar operating at about six miles per hour. The composition was sprayed from a knapsack sprayer atV 30 pounds per square inch at a rate of about 0.1 gallon per minute. In some tests the engine wheels were also sprayed and allowed to dry before starting. Control tests were also made in which no treatment was applied to the rails or to the wheels.

in a control test on a clear day Witha train consisting of two diesel units and 77 cars (60 loaded and 17 empty) having an adjusted gross tonnage of 4992 starting at an elevation of about 250 feet and going to an elevaton of around 400 feet over a distance of about 3 miles, 21 wheel slips were counted. Intermittent sanding -was used to increase traction but slipping was prevalent on the. entire grade.

Cm. a. subsequent clear day, after treating the rails.

ously described, a train consisting of 2 diesel units, 93 cars (-3 loade'd and 40 empty), having an adjusted tonnage of 5758, ascended the same grade with no rail slips and without using any sand. It will be noted that this train was 16 cars' longer than the train used in the control test. The maximum adhesion developed was about 24% on the lead unit. i

In a subsequent test ou a clear day with a train consisting of 2 diesel units and 80 cars (70 loaded and empty) having an adjusted tonnage of 6160, the train ascended the grade with no slips and without the use of sand. The maximum adhesion developed was 261% on the lead unit. In general, it was noted that the control adhesion with no sanding did not exceed about 11% and with sanding not more than about 18.5 adhe- .sion was obtained. Thus, the practice of the present invention greatly increased the efficiency of the. operation even without sanding.

Example X about 8. The isopropanol was added until it constituted=. 50% by volume of the composition. The resultant composition hereafter referred to as Composition V was a paste which Was applied to the tread of the locomotive Wheel through a V16 diameter copper tubing with the assistance of an air nozzle using 6 cubic feet of air per minute. The lead wheels of the two* trucks on the front unit were treated with this composition at the rate of 20 ounces applied to each of the left No. 1 and No. 3 wheels, 4 ounces applied to the right No. 1 wheel and 10 ounces applied to the right No. 3 wheel, on a train pulliug 80 cars and having 'an adjusted tonnage of 5002 over a distance of about three miies on a l.1% ascending grade. No slips were encountered and no sanding was required.

As previously indicated, the colloidal silica can be used in the practice of the invention in conjunction with auxiliary materials. been prepared for the purpose of the invention as follows:

Example XI Examp'le XII m A compostion wasprepared byV mixifng together 50 parts of a silica sol made by the Bird ion exchange method and containing 30% SiOz and 50 parts of kalin. The bearing surface of a steel rail coated with this composition. showed improved anti-Slip characteristics. 'i

Exa'mple Xl l l A composition was prepared by mixing together 50 parts of Waterglass having an NazOzSiOz ratio of 123.2 and 50 parts of kaolin. The hearing surface of a steel rail coated with this composition showed improved Iantislip characteristics. 'i

Example. XIV

A composition was prepared by mixing together 50 parts of waterglass of Example XIII and 50 parts of finely divided '87% Silica-13% alumina Catalyst lines with a fineness suchthat the averagey particle diameter was I mioron'orless. The hearing surface of. a steel rail coated with vthis composition showed improvedv anti-Slip characteristics.

For example, compositions have .af/sasse -13 Example XV Example XVI A composition was prepared by mixing together 50 parts of a 30% Silica sol and 50 parts of waterglass having an NazOzSiOz ratio of l:3.2. The hearing surface of a steel rail coated with this composition showed improved anti-Slip characteristics.

Example X Vll A composition was prepared by rnixing together 50 parts of waterglass having an NazOzSiOz ratio of 123.2 and 50 parts of jewelefis rouge. The bearing surface of a steel rail coated with this composition showed improved anti-Slip characteristics.

Example X VIII Compcsitions were prepared by incorporating with each of the compositions described in Examples I to IV and XI to XVII about 0.1 to 2% by weight of a finely divided electrical conductor such as carbon and finely divided powdered metals, e. g., iron and copper. These materials were incorporated in order to increase the electrical conductance of the coating. The hearing surface of a steel rail coated with these compositions showed an improved anti-Slip characteristic and also had better electrical conductance than the coated rail having no electrically conducting material added to the coating composition.

ln a similar manner, pasty to solid adhesion producing coating compositions can be prepared with other auxiliary materials, including, for example, the esterified silicas disclosed in U. S. 2,657,l49 by mixing such materials With colloidal silica. The best results have been obtained by using as auxiliary materials predominantly siliceous materials capable of forming particles in liquid suspension having an average diameter of l micron or less. The resultant compositions can be molded to a solid stick form and applied to a Wheel or rail by rubbing or other suitable means similar to those now employed in applying stick lubricants to wheel flanges. Suitable resins, plastics and other binders can be incorporated to produce and maintain the desired physical form.

Other materials which are capable of use in the invention are the solid silicas which are derived from silicic acid and silica sols. These solid silicas are extremely fine in particle size and are more accurately described as dehydrated colloidal silicas. The particle size of the preferred dehydrated colloidal silicas is preferably one micron or less but the aggregate form may be larger due to the drying techniques employed. Examples ofsuch materials are the solid surface esterified silicas, dried silica sols, silica gels and fine silica derived by dehydrating silicic acid.

lt will be seen from the foregoing discussion that the colloidal silica may be used in various physical forms including sols, semi-sols, gels, pastes and powders. It is also desirable to use a carrier which will assist in. distributing or dispersing the silica on the metal surface, the frictional contact of which it is desired to improve. The carrier is preferably water, a low molecular weight alcohol or other non-lubricating liquid. By non-lubrieating is meant that the liquid should have no substantially lubricating efiect. lt is possible, of course, for a liquid to have a slight lubricating effect which is more than counteracted by the adhesion-producing properties of the colloidal silica particles. In the practice of the invention,

however, the liquids preferably employed as a carrer ,medium for the colloidal silica are sufiiciently volatile at the temperatures used to permit the formation ofla semi-dry to dry coating which contains only minor proportions or substantially no residual carrier liquid.

In general, superior results are obtained by using cornpositions containing a silica sol as described under the heading A. Silica Sols. Good results are also obtained by employing the compositions described under the heading C. The Hydrolyzed Organic Esters of Silicic Acid The colloidal alkali metal silicates described under heading 15" hereof are generally less effective than the other materials mentioned when employed alone but their effectiveness is increased when they are used in conjunction with substances containing -finely divided discrete particles, such as fine clay (kaolin) and other finely divided water insoluble materials (e. g., inorganic silicates, oxides, and/or carbonates) as described in Examples XIV, XV, XVII, and XVIII.

While the invention has been illustrated with respect to improving the frictional contact between wheels and rails, it is contemplated that it can be applied generally to improving the frictional contact between two metal surfaces capable of motion one with respect to the other. In the case of locomotive wheels and rails, the improvement of frictional contact involves contacting parts which are normally in motion (or dynamic) during the period when optimum frictional contact is desired. However, the invention is also applicable to improving the frictional contact between a metal shaft and a sheave, gear or pinion frictionally mounted thereon. In this case, the colloidal silica, e. g., any of the compositions of Examples I to XVIII, is applied as a thin coating to the shaft and the frictionally mounted member is forced on the shaft so that the colloidal silica is between said member and the shaft. Similarly, the invention may be applied to form a layer, coating or film between bolts and locknuts, and also between other parts which are normally desired to remain static. In both dynamic and static applications the Optimum effect is obtained when the colloidal silica is presenton the metal surfaces in a semidry to dry state.

The present application is 'a continuation-in-part of my copending application Serial No. 484,171 filed January 26, 1955, and the disclosure of said application is incorporated herein as fully as if it had been set forth in its entirety.

The invention is hereby claimed as follows:

1. The method of improving the frictonal contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal silica, and bringing said surfaces into contact w-ith one another with said colloidal silica therebetween.

2. The method of improving the frictional contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal silica in a substantially non-lubricating carrier liquid, and bringing said surfaces into contact with one another with said colloidal silica therebetween.

3. The method of improving -the fric-tional contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying to -at least one of said surfaces a-thin coating of colloidal silica.

. with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal silica .in the form of a silica sol containing at least 3.0% SiOz,I 'and bringing said surfaces into .contact with one another 'with said colloidal Silica therebetweeen.

'avse/goes R v 5. The method of improving the frictional contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying to at least. one of Said surfaces a thin coating of colloidal silica Ltact with one another with said colloidal Silica therebetween.

7. The method of improving the frictional contact between two metal surfaces normally in rolling contact onel with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal Silica in the form of colloidalI Silica dispersed in a nonlubricating liquid comprising isopropanol and water, and bringing said surfaces into contact with one another with said colloidal Silica therebetween.

8. The method of improving the frictional contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal Silica in the form of colloidal Silica dispersed in a non-lubrieating liquid comprising methanol and water, and bringing said surfaces into contact with one another with said colloidal Silica therebetween.

9. The method of improving the frictional contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal Silica in the form of a coating of a Silica sol containing a finely divided silicate, and bringing said surfaces into contact with one another with said colloidalV Silica therebetween.

l10. The method of improving the frictional contact between -two metal surfaces normally in rolling contact one with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal :silicain .the form of a coating of a Silica sol containing :a finely divided kaolin, and bringing said surfaces into contact with one another with said colloidal Silica therebetween.

11. The method of improving the frictional contact between two metal surfaces' normally in rolling contact -one with respect to the other which comprises applying .to at least one of said surfaces a thin coating of colloidal :Silica in the form of a hydrolyzed organic ester of silicic acid, and bringing said surfaces into contact With one another with said colloidal Silica therebetween.

12. The method of improving the frictional contact between two metal surfaces normally in rolling contact one with respect to the other which comprises applying :to at least one of said surfaces a thin coating of colloidal Silica in the form of a hydrolyzed ethylfsilicate, and bringing said surfaces into contact with one another -with said colloidal silica therebetween.

13. The method of improving the frictional contact between two metal surfaces normally in rolling contact one with respect Lto the other which comprises applying to at least one of sa'id surfaces a -t'nin coating of colloidal.

one with respect to the other which comprises applying to at least one of said surfaces a thin coating of colloidal Silica in the form of an aqueous sodium silicate solution having an NazOzSiOz ratio within the range from about 123.2 to about 1:3.75 and containingla finely divided kaolin capable of forming particles in liquid suspension having an .average diameter not exceeding one micron,

and bringing said surfaces into contact with one another With said colloidal Silica therebetween.

15. A structure having two metal surfaces normally in rolling contact one with respect to the other and adapted to engage each other by frictional contact, at least one of said surfaces being coated with a thin coating of a .colloidal Silica.

16. A VStructure having two -metal surfaces normally in rolling contact one With respect to the other andV adapted to enga-ge each other by frictional contact, at least one of said surfaces being coated with a thin coating of a Semi-dry to dry coating of colloidal Silica.

17. A structure having two metal surfaces normally in rolling contact one with respect to the other and adapted to engage each other by frictional contact, at least one of said surfaces being coated with -a thin coating of a semi-dry to dry coating of colloidal Silica having an average particle size within the range from 1 to v mllimicrons.

18. A structure having two metal surfaces normally in roll-ing contact one with respect to the other and adapted to engage each other by frictional contact, at least one of said surfaces being coated with a thin coating of a Semi-dry to dry coating composition consisting predominantly of a siliceous material having an average diameter of not more than 1 micron and containing colloidal Silica having an average particle Size within the range from l to 150 millimicrons.

19. A structure having two metal surfaces normally in rolling contact one with respect to the other and adapted to engage each other by frictional contact, at least one of said 'surfaces being coated with a .thin coating resulting from allowing to dry thereon a coating of silica sol containing 3% to 48% SiOz.

20. A structure having two metal surfaces normally in rolling contact one with respect to the other and adapted to engage each other by frictional contact, at least one of said surfaces being coated with a thin coating resulting from allowing lto dry thereon a vaporizable liquid containing a hydrolyzed organic silicic acid ester.

21. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a thin coating of colloidal Silica.

22. The method of improving the frictional contact between railway Wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal Silica in a substantially nonlubricating Carrier liquid.

23. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the contacting surfaces thereof akthin coating of colloidal Silica in the form of a Silica sol.

24. The method of improving the frictional contac-t between railway wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a thin coating of colloidal Silica in the form of a Silica sol containing a-t least 3.0% .SiOz.

25. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal Silica in the form of a Silica sol containing from 7% to 48% SiOz.

26. The method of improving the frictional contact between railway wheels and tracksiwhich comprises applying to at least one of the Contacting surfaces thereof 21 lthin coating of colloidal Silica in the form of colloidal silica dispersed in a non-lubricating liquid Comprising a lower aliphatic monohydric alcohol and water.

27. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of colloidal silica dispersed in a non-lubricating liquid comprising isopropanol and water.

28. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of colloidal silica dispersed in a non-lubricating liquid comprising methanol and water.

29. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of a coating of a silica sol containing a finely divided silicate.

30. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of a coating of a silica sol containing a finely divided kaolin.

31. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surface-s thereof a thin coating of colloidal silica in the form of a hydrolyzed organic ester of silicic acid.

32. The method of improving the frictional contact between railway wheels -and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of a hydrolyzed ethyl silicate.

33. The method of improving the friction-al contact between railway wheels and tracks which comprises applying 4to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of an aqueous sodium silicate solution having an Na20:SiO2 ratio within the range from about 1:3.2 to about 1:3.75 and containing a finely divided predominantly siliceous maten'al Capable of forming particles in liquid suspension having an average diameter not exceeding one micron.

34. The method of improving the frictional contact between railway wheels and tracks which Comprises applying to at least one of the Contacting surfaces thereof a thin coating of colloidal silica in the form of an aqueout sodium silicate solution having an NazOzSiOz ratio Within the range from about 1:3.2 to about 1:3.75 and containing a finely divided kaolin capable of forming particles in liquid suspension having an average diameter not exceeding one micron.

35. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contact-ing surfaces thereof a thin liquid coating of colloidal silica in the form of a silica sol, at least partially drying said coating and bringing said surfaces into contact with one another with said coating of colloidal silica therebetween.

36. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at fleast one of the Contacting surfaces thereof a thin liquid coating of colloidal silica in the form of a silica sol resulting from acidifying an aqueous silica sol containing 7% to 48% by weight Si02 in a colloidal state and adding a lower aliphatic monohydric alcohol thereto, at least partially drying said coating and bringing said surfaces into contact with one another with said coating of colloidal silica therebetween.

37. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin liquid coating of colloidal silica in the form of a silica sol resulting from acidifying an aqueous silica sol containing 7% to 48% by weight SiOz in a colloidal state with phosphoric acid and adding a lower aliphatic monohydric alcohol, at least partially drying said coating and bringing said surfaces into contact with one another with said coating of colloidal silica therebetween.

38. The method of improving the frictional contact between railway wheels and tracks which comprises applying to at least one of the Contacting surfaces thereof a thin liquid coating of colloidal silica in the form of a silica sol resulting from acidifying an aqueous silica sol containing 7% to 48% by weight Si02 in a colloidal state with phosphorc acid to a pH of about 3.5 and adding isopropanol thereto until the isopropanol content is approximately 50% of the total volume, at least partially drying said coating and bringing said surfaces into contact with one another with said coating of colloidal silica therebetween.

39. A railway rail having its wheel bearing surface coated with a thin coating of a colloidal silica.

40. A railway rail having its wheel bearing surface coated with a thin coating of a semi-dry to dry coating of colloidal silica having an average particle size from 1 to millimicrons.

41. A railway rail having its wheel bearing surface coated with a thin coating resultling from allowing to dry thereon a coating of silica sol containing 3% to 48% SiOz.

42. A railway rail having its wheel hearing surface coated with a thin coating resulting from allowing to dry thereon a coating of acidified silica sol containing a lower aliphatic monohydric alcohol.

43. A railway rail having its wheel bearing surface coated with a thin coating resulting from allowing to dry thereon a coating of acidified silica sol containing phosphoric acid and isopropanol.

Connol'ly Apr. 17, 1928 Kirk Oct. 1, 1946 

1. THE METHOD OF IMPROVING THE FRICTIONAL CONTACT BETWEEN TWO METAL SURFACES NORMALLY IN ROLLING CONTACT ONE WITH RESPECT TO THE OTHER WHICH COMPRISES APPLYING TO AT LEAST ONE OF SAID SURFACES A THIN COATING OF COLLODIAL 